45 degree chamfered on two corners
A square nut having a concave face and a concave or slotted top.
NSN 6135-01-386-5709
NSN 5855-00-198-3197
NSN 5985-01-119-4155
NSN 4140-01-548-8735
NSN 5950-01-198-9512
NSN 5915-00-202-5192
NSN 6105-00-043-5446
NSN 6620-01-440-9810
NSN 5945-00-676-8446
NSN 5998-01-299-1680
NSN 5945-01-445-6081
NSN 2925-00-859-8579